21 We can now answer the question, how we know that these books were written by the apostles. In a word, we know this in the same way that you know that the books whose authority you are so deluded as to prefer were written by Manichæus. For, suppose some one should raise a question on this point, and should contend, in arguing with you, that the books which you attribute to Manichæus are not of his authorship; your only reply would be, to ridicule the absurdity of thus gratuitously calling in question a matter confirmed by successive testimonies of such wide extent. As, then, it is certain that these books are the production of Manichæus, and as it is ridiculous in one born so many years after to start objections of his own, and so raise a discussion on the point; with equal certainty may we pronounce it absurd, or rather pitiable, in Manichæus or his followers to bring such objections against writings originally well authenticated, and carefully handed down from the times of the apostles to our own day through a constant succession of custodians.
Source: Reply to Faustus the Manichaean (New Advent)